Effect of stress ratio and test methods on fatigue crack growth rate for nickel based superalloy Udimet720

This paper investigates the influence of stress ratio on fatigue crack grow th (FCC) rates in the Paris region and at room temperature for nickel based superalloy Udimet720 under two control modes: constant Delta P and constan t Delta K. The effect of stress ratio on FCG rate for this alloy is modeled using the Walker equation by considering the tensile load range only in th e case of the negative stress ratio. The study shows that the constant Delt a K test generates more accurate definition of parameters in the Walker equ ation and leads to more accurate prediction of the FCG rate at different st ress ratio. The paper indicates that the effectiveness of modeling stress r atio effect is, in part, dependent on the quality of test data obtained by different test methods. (C) 1999 Elsevier Science Ltd. All rights reserved.